The present invention relates to a method of adhering wafers, e.g., silicon wafers, onto a carrying plate of a surface polishing machine with an adhesive or water and an wafer adhering device for said method.
In a wafer polishing machine, wafers are adhered onto a tough plate called a carrying plate so as to handle wafers. Surfaces of the wafers, which have been adhered on the carrying plate, are polished by a polishing unit. Wafers are thin, so they are apt to be curved and it is difficult for wafers to maintain flat. By holding wafers on the carrying plate, they can be maintained flat and polished properly.
To polish and make surfaces of wafers highly flat, wafers are required to be highly flatly adhered onto the carrying plate, and the surface of the carrying plate must be highly flat. Especially, in the case of polishing silicon wafers, a plurality of silicon wafers, which have been adhered on the polishing plate, are pressed onto a polishing plate, then the carrying plate and the polishing plate are relatively moved to polish surfaces of the silicon wafers. Accuracy of flatness of the silicon wafers and the surface of the carrying plate should be high, e.g., submicron order.
The polished wafers are peeled from the carrying plate and conveyed to the next step. The carrying plate is washed to reuse many times. Therefore, carrying plates should have higher durability, so they are made of tough and durable materials, e.g., ceramics.
Note that, in the case of adhering wafers with an adhesive, e.g., wax, the wafer is adhered onto the surface of the carrying plate by the steps of: dropping the wax onto a surface of the wafer; spinning the wafer so as to uniformly coat the whole surface of the wafer; inverting the wafer; and adhering the wafer onto the surface of the carrying plate.
Conventionally, wafer adhering positions, at which a plurality of wafers are respectively adhered, on the circular carrying plate are separated with regular angular spaces. In one case, a first wafer adhering position, from which the first wafer is adhered, is not defined on the carrying plate; in another case, the first wafer adhering position is defined thereon and wafers are adhered on the fixed wafer adhering positions in predetermined order. If wafers are adhered at the fixed positions in predetermined order, wafers can be polished, at each wafer adhering position, under the same adhering condition. By polishing under the same condition, tendency of polishing accuracy at each wafer adhering position can be known, so the polishing accuracy, etc. can be easily controlled.
However, in the case of adhering wafers at the fixed wafer adhering positions in the surface of the carrying plate, a surface condition of the fixed wafer adhering positions will be quite different from that of other parts of the carrying plate because of chemical agents. Namely, the wafer adhering positions of the carrying plate are usually coated with the adhesive; other parts thereof are exposed in a liquid abrasive, e.g., slurry. The parts exposed in the abrasive are eroded by the abrasive, so surface condition between the wafer adhering positions and other parts are quite different.
Since the surface condition is partially different in the carrying plate, the partial difference badly influences the polishing accuracy, and maintenance of the carrying plate is frequently required.
As described above, the tendency of the polishing accuracy at each wafer adhering position can be known by adhering wafers at the fixed wafer adhering positions in predetermined order, and the polishing accuracy can be easily controlled. But, if the surface condition of one of the wafer adhering positions is bad, wafer adhered at the bad adhering position are always badly polished, and manufacturing efficiency must be lower.
On the other hand, if the first wafer adhering position is not defined on the carrying plate or wafers are freely adhered thereon, the polishing accuracy at each wafer adhering position cannot be controlled at all, so that the flatness of the surface of the carrying plate is made worse and the polishing accuracy is made lower.
If wafers are freely adhered onto the surface of the carrying plate, the surface of the carrying plate is not uniformly used, so that said difference between the wafer adhering positions and other parts is apt to be occurred. Thus, the flatness of the surface of the carrying plate must be frequently corrected. The whole surface of the carrying plate cannot be used properly, and span of life of the carrying plate will be shorter.
In the case of adhering wafers at the fixed wafer adhering positions, a standard position of the carrying plate must be detected by detecting a mark of the carrying plate. But the mark cannot be detected efficiently, so manufacturing efficiency cannot be improved.
An object of the present invention is to provide a method of adhering wafers and a wafer adhering device, which are capable of uniformly using whole surface of a carrying plate, improving the polishing accuracy of wafers and extending span of life of the carrying plate.
Another object of the present invention is to provide a wafer adhering device, which is capable of quickly detecting a standard position of the carrying plate and improving the manufacturing efficiency.
To achieve the objects, the present invention has following structures.
In the present invention, the method of adhering a plurality of wafers onto a surface of a carrying plate with predetermined spaces is characterized by, regularly shifting wafer adhering positions, at which said wafers are respectively adhered, with respect to a standard position of the carrying plate.
In the method, the carrying plate may be a circular plate, the wafers may be initially adhered at initial adhering positions on the surface of the circular carrying plate with regular angular spaces, and the wafer adhering positions may be respectively returned to their initial adhering positions when each wafer adhering position reaches the adjacent initial wafer adhering position. With this feature, the wafer adhering positions can be properly angularly shifted, and angle of shifting the wafer adhering positions can be minimum so manufacturing efficiency can be improved.
The wafer adhering device for adhering a plurality of wafers onto a surface of a carrying plate with predetermined spaces, comprises:
an adhering head positioning the wafers at wafer adhering positions in the surface of the carrying plate, the adhering head pressing the wafers onto the carrying plate;
an adjusting mechanism being capable of adjusting relative positional relationship between the adhering head and the carrying plate;
a mark being provided at a standard position of the carrying plate;
a sensor detecting the mark; and
a control unit detecting the standard position of the carrying plate by the sensor, the control unit controlling the adjusting mechanism so as to regularly shifting the wafer adhering positions with respect to the standard position of the carrying plate.
In the device, the mark may include an identification code for individually identifying the carrying plate. With this feature, a plurality of carrying plates can be properly managed.
In the device, the identifying mechanism may include a rotary table holding and rotating the carrying plate. With this simple structure, wafers can be adhered at desired positions.
Further, the wafer adhering device for adhering a plurality of wafers onto a surface of a carrying plate with predetermined spaces, comprises:
an adhering head positioning the wafers at wafer adhering positions in the surface of the carrying plate, the adhering head pressing the wafers onto the carrying plate;
a rotary mechanism including a rotary table for holding and rotating the carrying plate, the rotary mechanism being capable of detecting and adjusting relative positional relationship, in the circumferential direction of the carrying plate, between the adhering head and the carrying plate;
a mark being provided at a standard position of the carrying plate;
a plurality of mark detecting means for detecting the mark; and
a control unit detecting the standard position of the carrying plate by one of the mark detecting means, the control unit controlling the rotary mechanism so as to indexing the wafer adhering positions on the carrying plate.
In the device, even-number of the mark detecting means may be symmetrically arranged with respect to the carrying plate. With this feature, the wafer adhering positions can be indexed efficiently.
In the present invention, the wafer adhering positions are regularly shifted, with respect to the standard position of the carrying plate, in the surface of the carrying plate, so that the wafer adhering positions can be properly managed. The whole surface of the carrying plate can be uniformly used, so that the surface conditions of the wafer adhering positions, which are regularly shifted, can be uniformly maintained. Therefore, wafers can be stably adhered on the carrying plate, the polishing accuracy of the wafers can be improved, and the span of life of the carrying plate can be extended.
Further, by employing a plurality of mark detecting means, the mark can be quickly detected by one of the mark detecting means and the wafer adhering positions can be quickly indexed. Therefore, the wafer adhering positions in the surface of the carrying plate can be efficiently indexed, and the manufacturing efficiency can be improved.